Marty,
You only option to upgrade the processor is by replacing the motherboard with a compatible one.
I am not sure that it will justify the investment.
I will recommend you to access the motherboard and find the exact model. Then check in Ebay for compatible replacement (including a different processor).
I could not find any documentation from Sony sharing technicalities to make our job better (as technicians).
You could try reaching team to see the official version.....in my opinion they will say that there is no way to upgrade.
Good luck and good repair.
JM - Montreal